Self-destruct fuze with electrostatic switch

ABSTRACT

A self-destruct time device has a resistance shunted capacitor charged by a power supply, prior to launch of a munition, through a normally open latching spin switch and an intermittently normally closed single pole electrostatic switch. The power supply is automatically disconnected from the projectile as soon as the munition is launched. A detonator, connected into a timing circuit by the spin forces of a launched projectile, is subsequently fired after projectile impact when the electrostatic switch is reswitched, as a function of the RC time constant, from its open position to its normally closed position because of reduced electrostatic force on its pole piece.

United States Patent [191 Valatka et a].

[ June 25, 1974 1 SELF-DESTRUCT FUZE WITH ELECTROSTATIC SWITCH [75] Inventors: Daniel E. Valatka, Sparta; Bernard Fairbanks, Stanhope, both of NJ.

22 Filed: Jan. 23, 1973 21 Appl. No.: 325,962

[52] US. Cl l02/70.2 R [51] Int. Cl...... F42c 11/06, F42c 9/00, F42c 11/00 [58] Field of Search 200/181; 320/1; 102/702 [56] References Cited UNITED STATES PATENTS 2,175,354 10/1939 Lewin 200/181 2,644,398 7/1953 Rabinow 102/702 R 2,744,976 5/1956 Black 102/702 R 3,610,153 10/1971 Betts 102/702 A 3,721,860 3/1973 Phinney 320/1 POWER SUPPLY 3,722,416 3/1973 Lunt et a1 102/702 P Primary Examiner-Benjamin A. Borchelt Assistant Examiner-Th0mas H, Webb Attorney, Agent, or Firm-Edward J. Kelly; Herbert Berl; A. Victor Erkkila [57] ABSTRACT A self-destruct time device has a resistance shunted capacitor charged by a power supply, prior to launch of a munition, through a normally open latching spin switch and an intermittently normally closed single pole electrostatic switch. The power supply is automatically disconnected from the projectile as soon as the munition is launched. A detonator, connected into a timing circuit by the spin forces of a launched projectile, is subsequently fired after projectile impact when the electrostatic switch is reswitched, as a function of the RC time constant, from its open position to its normally closed position because of reduced electrostatic force on its pole piece.

2 Claims, 5 Drawing Figures PAIENIEDJUNZBIHH 581 ,8545

/ SHEEI 1 0F 2 POWER SUPPLY SELF-DESTRUCT FUZE WITH ELECTROSTATIC SWITCH GOVERNMENTAL INTEREST The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without the payment to us of any royalty thereon.

BACKGROUND OF THE INVENTION Various means have been used in the prior art to provide means for the self-destruction of duds that failed to fire on impact. The elimination of duds from the battlefield, by self-destruction, has become more important in recent years because of the proliferation of large number of scatter mines delivered by clustered small artillery. It is sometimes necessary to rid a target area of duds, to prevent the injury of friendly troops subsequently passing through the area, and to deny the enemy the use of duds which he can rework and use as a secondary source of ammunition. The problem with prior art devices, using mechanical self-destruct timers,

is that they are generally large in size, fail in accuracy,

and unable to withstand the environmental forces of launch and impact. The problem with prior art electronic self-destruct devices has been that they require a reserve battery to provide continuous current during the self-destruct period of operation. The use of such batteries in self-destruct devices is both costly and space consuming thus reducing the available payload capability and the projectile or mine lethality.

SUMMARY OF THE INVENTION The present invention relates to a self-destruct fuze which causes a munition to explode a fixed interval of time after the munition has impacted on the target and failed to explode on impact. The present invention is designed to prepare a munition, such as a projectile or a mine, which has been given spin during launch to improve its ballistic trajectory, for self-destruction after failing to explode on impact. A voltage is applied to the input of a self-destruct fuze which charges a resistance shunted capacitance through an intermittently normally closed single pole electrostatic switch. The supply voltage which charges the capacitance is connected across the electrostatic pole means terminal and the conductive terminal of the normally closed electrostatic switch. The electrostatic forces generated between these two members as a result of proximity of the movable pole means to the insulated terminal and the voltage therebetween is sufficient to pull the pole means toward the insulated terminal overcoming the mechanical bias tending to hold the pole means in the normally closed position. The capacitor is charged during the time that the projectile is in the launching device. When the projectile reaches sufficient angular acceleration the normally open spin switch changes from its normally open position to a closed latched position and connects the detonator with which it is in series so that it is in parallel connection across the capacitance through the now open, intermittently normally closed terminal of the electrostatic switch. When the voltage of the capacitance falls due to the drop in voltage caused by a parallel resistor, the restoring force of the mechanical bias on the pole means overcomes the reduced attractive electrostatic force between the pole means and the insulated terminal thereby causing the residual charge across the capacitor to be placed across the series combination of detonator and closed spin switch, thus causing the latter to initiate and explode the projectile. V

The present invention is reliable in its operation, small in size, relatively cheap to manufacture, can utilize a standard high energy detonator, does not require a reserve battery to accompany the device, is storable for an indefinite period over a wide temperature range, has a timing accuracy of i 10 percent over a temperature range of 35C to C, permits non-destructive timing checks to be made, and is rugged enough to perform as required after both launch and impact.

One of the objects of this invention is to provide a self-destruct fuze for a munition that is fired from a rifled launching device and fails to explode after a fixed interval of time after impact.

Another object of this invention is to provide an electrically self-destruct fuze which will function without the need of a reserve battery.

Another object of this invention is to provide an electrically operated self-destruct fuze which is storable for an indefinite period over a temperature range of 35C to +75C.

Another object of this invention is to insure the operation of an electrically operated self-destruct fuze which has a timing accuracy of i 10 percent over a temperature range of 35C to +75C.

Another object of this invention is to provide an electrically operated self-destruct fuze which can utilize a conventional power source to fire: a standard high energy detonator.

Another object of this invention is to provide an electrically operated self-destruct fuze whose dominant failure mode will not cause late self-destruct time delays.

A further object of this invention is to provide an electrically operated self'destruct fuze which will, because of its ruggedness, reliably reduce the number of duds remaining on a target area after the projectile has impacted.

For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic circuit drawing of the selfdestruct fuze showing the position of the spin and the electrostatic switch prior to the munition being launched.

FIG. 2 is a schematic diagram of the intermittent normally closed single pole double throw electrostatic switch.

FIG. 3 is a plan view of the electrostatic switch.

FIG. 4 is a partial cross-sectional view taken along line 44 of FIG. 3. v

FIG. 5 is a partial cross-sectional view taken along line 5--5 of FIG. 3.

Throughout the following description like reference numerals are used to denote like parts of the drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 the self-destruct fuze circuit 3 contained in the munition after launch is shown to the right of the dashed line 10. While the munition is in the launching device a power supply 12 is connected to the pair of input terminal plugs 14 and 16 of the selfdestruct fuze 18 through a matched and aligned pair of sliding contacts 20 and 22. Prior to launch the power supply 12 having an output voltage V charges the parallel capacitor 24 and resistor 26 at a first common junction 25 thru an electrostatic intermittent normally closed switch 28 by means of a first electrical connector 30, thru a first fixed contact 32, movable contact or pole piece 34, pole piece fixed contact 35 and connector 36, and to the second common junction 27 thru electrical connector 38, to a voltage V. A detonator 40 in series with a normally open single pole single throw latching spin switch 42 is connected at common junctions 44 and 46 to the electrical connectors 30 and 38 respectively. When a direct current supply voltage is applied to the pair of input terminal plugs 14 and 16, an electrostatic force is created, between the pole piece 34 and the second insulated fixed contact terminal 48 of the electrostatic switch 28, which is sufficient to move the mechanically biased pole piece 34 to its open position shown by dotted line 50 against the anodized insulating surface 52 of the second insulated fixed terminal 48. The insulated second contact terminal 48 is electrically connected to the second capacitance common junction 27 through conductor 49. As soon as the munition is launched the pair of input terminal plugs 14 and 16 and pair of sliding contacts 20, 22 to the left of the dashed line are separated thereby disconnecting the fuze 18 from the power supply 12. After the pole piece moves to the dashed line position 50 and when the munition gains sufficient angular accelerations the normally open latching spin switch closes putting the detonator into the circuit at common junctions 44 and 46. The pole piece 34 remains switched against the insulated second contact terminal 48 until such time as the voltage V across the capacitor decays to the unswitching voltage V the time to reach this latter voltage is a function of the RC time constant of the resistor 26 and the capacitance 24 and the parallel leakage resistance across the pole piece 34 and the second insulated fixed terminal 48 of the electrostatic switch. At V V,, the electrostatic attraction becomes too weak to keep the pole piece 34 switched against the second insulated fixed terminal 48, whereupon the pole piece 34 switches back to the first contact terminal 32 dumping energy E, 1/2 C V into the detonator 40 thus completing the self-destruct mission. The self-destruct time T, is given by the equation T,, RC log V u,

where V= V e where V 160 V and R 20 G0 and C= .33 Mfd and V 59 V 4 and having an area A equal and essentially parallel to A.

3. The first fixed contact terminal 32 is represented as imposing an initial deflection Y, on the flexible movable contact or pole piece 34 from its free position 54.

where D= free gap distance between the free position 54 of pole piece 34 and the conducting surface of the second contact terminal.

Y the deflection of the pole piece 34 after it has switched from its free position 54 to the anodized insulator 52 S the thickness of insulator 52 'y= the relative dielectric constant of. the insulator 52 ('y a l e permittivity of air K spring rate of the biased pole piece 34,

Then V the unswitching voltage is given as V,, s/y V KYu/( o V,, the minimum voltage required for switching depends upon the initial deflection in the following manner:

The electrostatic switch 28 is characterized by a critical deflection Y where Y =D/3 S/3 (l l/y) and Y,=D/3 fory=l If Y /Y 1, then V, 2 VK YR/(e A/2) c 0 A neglecting fringing effects and assuming that D the characteristic linear dimension of A.

Referring now to FIG. 3, the electrostatic switch 28 has an insulated mounting board 56 which has pole piece fixed contact 35 mounted thereon by rivets 58, 58. The cantilever shaped pole piece 34 has its fixed end 37 mechanically and electrically connected to the fixed contact 35 by a screw 62 and the pole piece free end 39 is normally biased against the first contact terminal 32. The second terminal 48 is fixed to the insulated mounting board 56 by rivets 60, 60. The second insulated fixed terminal 48 has an anodized insulated layer 52 on its peripheral surface which insulates the pole piece free end 52 from the second insulated fixed terminal 48 when the former is drawn to the latter by an electrostatic force.

FIG. 4 shows a partial cross-sectional view taken through line 44 of FIG. 3. The second insulated fixed terminal 48 is held by rivets 60, 60 in close proximity to the movable free end 39 of the pole piece 34. The pole piece 34 is a leaf spring resiliently biased against the fixed terminal 32.

FIG. 5 is a partial cross-sectional view taken along line 5-5 of FIG. 3 showing how the pole piece fixed contact 35 is fixed to the mounting board 56 by rivets 58 and 58 (not shown) and how the pole piece fixed end 37 is held to the fixed contact 35 by the screw 62.

understood that we do not desire to be limited to exact detailsof construction shown and described for obvious modifications will occur to a person skilled in the art.

Having thus fully described the invention, what is claimed as new and desired to be secured by Letters means for electrically connecting said power supply to said fuzeprior to launch of said munition and for disconnecting said power supply from said fuze at launching which includes;

a pair of input terminal plugs having a first terminal electrically connected with said first contact terminal, a second terminal electrically connected to said second insulated fixed terminal; and

a pair of sliding contacts electrically connected to the output of said power supply, each in electrical contact with one of said pair of input terminal plugs prior to the launch of said munition;

time delay charging means electrically connected in parallel with said power supply; spin response detonating means electrically connected in parallel with said charging means; means, including an electrostatic switch, for switching said charging means to said detonating means for exploding said munition after it fails to explode after said fixed interval of time which includes; an intermittent normally closed electrical switch including a first fixed contact terminal, a biased movable contact having two opposite active surfaces one of which has an area at least equal to A, a second insulated fixed terminal having a predetermined area of A equal to A, coated with a layer of insulating material facing one of said movable contact surfaces, said layer having a thickness S and dielectric constant 'y, said other active surfaces of said movable contact facing said first fixed contact temiinal and in spring biased contact therewith and having a spring rate K; and

a resistor and capacitor, having predetermined resistance R and capacitance C respectively, connected in parallel with each other and with said movable contact and said second insulated fixed contact terminal, whereby said capacitor is charged to a voltage V V, at launch, which causes said biased movable contact to be moved into contact with said second insulated fixed terminal, and V to decay to the unswitching voltage V,, in time T RC log V /V at which time the electrostatic attraction between said biased movable contact and said second insulated fixed contact terminal becomes too weak to keep said biased movable contact in contact with said second insulated fixed contact terminal thereby releasing said biased movable contact to contact said first fixed contact, thereby dumping energy E,, l/ CV into said detonator and to explode the same.

2. A self-destruct fuze as recited in claim 1 wherein said spin responsive detonating means comprises;

nected to said second fixed terminal.

- UNITED STATES PATENT OFFICE CERTIFICATE 'OF CORRECTION Patent No- 3 818 835 25 lune l9J L Inventor(s) Daniel E. Va'latka and Bernard Fairbanks It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In column 3, line 5 2, and in column 6, line 18, "log should read "log In column 3, line 53, "V should read ---V igma aaa gna mi 29% day of dem 1974;

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents FORM F'0-1050 (10-69) USCOMM-DC 60876-P69 fir U.S. GOVERNMENT PRINTING OFFICE: I969 0-356-33,

, r UNITllD STATES PATENT OFFICE I CERTIFICATE OF CORRECTION Patent No. 3 818 85 25 lnne l91.4

Inventofls) Da nie'l E. Va'latka and Bernard Fairbanks It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In column 3, line 52, and in column 6, line 18, "log should read --log In column 3, line 53, "V should read ---V Signed aaa' galsa this 29th "day or October 1974*.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents f FORM PO-1050 (10-69) USCOMM-DC: 60376-P69 u.s. GOVERNMENT PRINTING orrlc: an man-5:4. 

1. A self-destruct fuze for electrically exploding a munition a fixed time interval after launch which comprises: a power supply having a predetermined voltage Vo; means for electrically connecting said power supply to said fuze prior to launch of said munition and for disconnecting said power supply from said fuze at launching which includes; a pair of input terminal plugs having a first terminal electrically connected with said first contact terminal, a second terminal electrically connected to said second insulated fixed terminal; and a pair of sliding contacts electrically connected to the output of said power supply, each in electrical contact with one of said pair of input terminal plugs prior to the launch of said munition; time delay charging means electrically connected in parallel with said power supply; spin response detonating means electrically connected in parallel with said charging means; means, including an electrostatic switch, for switching said charging means to said detonating means for exploding said munition after it fails to explode after said fixed interval of tIme which includes; an intermittent normally closed electrical switch including a first fixed contact terminal, a biased movable contact having two opposite active surfaces one of which has an area at least equal to A, a second insulated fixed terminal having a predetermined area of A'' equal to A, coated with a layer of insulating material facing one of said movable contact surfaces, said layer having a thickness S and dielectric constant gamma , said other active surfaces of said movable contact facing said first fixed contact terminal and in spring biased contact therewith and having a spring rate K; and a resistor and capacitor, having predetermined resistance R and capacitance C respectively, connected in parallel with each other and with said movable contact and said second insulated fixed contact terminal, whereby said capacitor is charged to a voltage Vo V, at launch, which causes said biased movable contact to be moved into contact with said second insulated fixed terminal, and V to decay to the unswitching voltage Vu in time Tu RC logn Vo/Vu, at which time the electrostatic attraction between said biased movable contact and said second insulated fixed contact terminal becomes too weak to keep said biased movable contact in contact with said second insulated fixed contact terminal thereby releasing said biased movable contact to contact said first fixed contact, thereby dumping energy Eu 1/2 CVu2 into said detonator and to explode the same.
 2. A self-destruct fuze as recited in claim 1 wherein said spin responsive detonating means comprises; a detonator electrically connected in series with a normally open latching spin switch, said detonator having one of its terminals electrically connected to said first fixed contact terminal and said spin switch having one of its terminals electrically connected to said second fixed terminal. 